1. Field of the Invention
The present invention relates to a flat panel display device, and more particularly to a picture quality controlling method that improves a picture quality using a repair process and a compensation circuit together, and a flat panel display device using the same.
2. Description of the Related Art
Flat panel display devices are light in weight and can be made small in size compared to a cathode ray tube. The different type of flat panel display devices include a liquid crystal display, a field emission display, a plasma display panel, an organic light emitting diode, etc. Further, the flat panel display device includes a display panel for displaying a picture.
In addition, during a testing process, the display panel is sometimes found to have a defect. One example of a defect is a defect sub-pixel appearing in the test process. In more detail, the defect sub-pixel is generated by a short and open of a signal line, a defect of a thin film transistor (“TFT”), a defect of an electrode pattern, etc. In addition, the defective sub-pixel appears as a dark spot or bright spot on the display screen.
Further, because a bright spot is seen easier than a dark spot, a defect sub-pixel appearing as a bright spot is made to be a dark spot to overcome this problem. Also, as shown in FIG. 1A, a defect sub-pixel made to be the dark spot is essentially not perceived in the display screen using a black gray level. On the contrary, as shown in FIGS. 1B and 1C, the dark defect sub-pixel made as a dark spot is clearly perceived in a display screen using a middle gray level and white gray level, respectively.
Another defect detected during the testing process is caused by a non-uniformity of brightness of a backlight unit. Thus, the panel defect appears as a display stain having a brightness difference on the display screen. That is, if the same signal is applied to a normal area and a panel defect area of the display panel, a picture displayed in the panel defect area is displayed to be darker or brighter than the picture displayed in a normal area. In addition, the defect area may also have a different color impression than a normal area.
Further, the panel defect is mostly generated during the display panel fabrication process. The defect also generally has a fixed form such as dot, line, belt, circle, polygon, etc. or has an undetermined form in accordance with what caused the defect. For example, FIGS. 2A to 2E illustrate different defect shapes. In addition, among the defects shown in FIGS. 2A to 2E, the vertical belt shape defect shown in FIGS. 1A to 1C is mainly generated by an overlapping exposure process, a number difference of lens, etc.
Also, the dot shape panel defect shown in FIG. 2D is mainly generated by impurities, etc. The panel defect may also cause a defect in the overall product. This defect also decreases the amount of produced flat panel displays thereby increasing the manufacturing costs. Further, even though a product having a defect may be shipped as a good product (i.e., because the defect is below a particular threshold), the picture quality deteriorated due to the panel defect reduces the reliability of the product. Accordingly, various methods have been proposed to improve the picture quality caused by the panel defect. However, the related art improvement methods focus mainly on solving problems in the fabrication process.
In addition, the brightness non-uniformity caused by a backlight unit is also a possible picture quality defect appearing in the liquid crystal display device. That is, the liquid crystal display device is not a self-luminous device, and thus irradiates light to the display panel using the backlight unit. The liquid crystal display device also controls the transmittance of the light traveling from the rear surface of the display panel to the front surface thereby displaying a picture. However, the backlight unit causes display problems in the liquid crystal display device. For example, the backlight unit sometimes causes a problem in that various shapes appear on the display screen, e.g., a bright line, because the light from the backlight unit is not uniformly incident to the entire incidence surface of the display panel.
For example, FIG. 3 represents an example of bright lines appearing in the liquid crystal display device using a direct type backlight unit. The related art tries to solve this problem by improving an operation or structure of the backlight unit, which is difficult.
Other various picture quality defects may also be found in the flat panel testing process. Further, the above discussed picture quality defects may also appear to be overlapped in one flat panel display device.